The present invention relates to the field of semiconductor components, and, more particularly, to a probe tip card for testing components on a semiconductor wafer.
To reduce manufacturing costs and times, a majority of tests performed on semiconductor components, i.e., integrated circuits and discrete components, are presently carried out directly on the silicon wafers when they come off the production line before the cutting operation. To perform the tests, a tester provides electrical signals to the integrated circuit chips using a probe tip card adapted to their topology. For this purpose, the silicon wafer containing the chips to be tested is moved towards the probe tip card so that the probe tips, or needles, rest on the contact pads provided on the chips. The probe tip card is part of a testing machine. A processor is used for the automatic management of the testing machine. It also provides for the running of the test sequences, the storage of the test results, and the identification of defective chips.
There are three kinds of commonly used probe tip cards. They are manufactured according to three different technologies. These technologies are known as the xe2x80x9ccantileverxe2x80x9d technology, the xe2x80x9cmembranexe2x80x9d technology, and the xe2x80x9cverticalxe2x80x9d technology.
A probe tip card made according to the xe2x80x9ccantileverxe2x80x9d technology is shown schematically in a sectional view in FIG. 1A, and in a top view in FIG. 1B. A probe tip card 10 of this kind has several needles 11 positioned horizontally, i.e., parallel to the surface of the card, and around a window 15 formed in the center of the probe tip card 10. This type of card is generally connected to an epoxy or ceramic printed circuit support 12. The needles 11 are fixed to the support 12 either by soldering or by bonding with an epoxy adhesive (reference 13). Conductive wires 16 are used for the electrical connection of the needles 11 to the tester 19 by the contacts of the printed circuit.
For greater clarity, only one chip 21 to be tested is shown in the silicon wafer 20 in FIG. 1A. This chip has contacts 22. During the tests, the silicon wafer 20 is moved towards the probe tip card 10 so that the needles 11 are supported on the contact pads 22, and thus provide an electrical contact between the chip 21 and the tester 19 through the probe tip card 10.
The shape of the needles 11 allow for a certain elasticity. A retention ring 14 is used to hold the needles so that they are pointed towards the contacts 22 of the circuit to be tested. Furthermore, the ends of the needles 11 are curved to form a claw. Thus, during the tests, when the contacts 22 of the chips to be tested are pressed against the needles 11 of the probe tip card 10, the pressure provides a side motion of the needles 11. This side motion prompts a clawing effect on the contacts 22. This clawing enables the removal of a surface layer of aluminum oxide that is formed over the contacts 22, and thus enables very high quality electrical contact to be established.
A card of this kind allows for the performance of up to 700,000 tests. However, its cost of manufacture is still quite high. A major drawback related to the use of these probe tip cards 10 is that their handling requires great precautions. The needles 11 exert a large amount of force on the contacts 22 of the chips 21. Care is needed to avoid applying excessive pressure when the chips 21 to be tested and the probe tip card 10 come into contact with each other to avoid damaging the contacts of the chips 21. Such damage could cause the breakage of the passivation layer around the contact pads 22. This deterioration of the contact pads 22 for the chips 21 would present problems since a chip 21 requires tests at different stages of its assembly into modules. Consequently, the number of tests are limited to prevent excessive deterioration of the chip 21 caused by the testing operation itself.
The ends of the needles 11 must be located in the same plane so that each of them can set up an electrical contact with a contact pad 22 of a chip 21 being tested. This planar characteristic may be obtained by working on the shape of the needles 11 after they have been fixed in the probe tip card 10. The trueing, however, is a laborious and lengthy task. Furthermore, this trueing of the needles 11 often deteriorates after the needles 11 have been pressed between the contact pads 22 because they tend to buckle. As a result, constant maintenance is required.
Furthermore, even an accurate trueing of the needles 11 cannot compensate for the significant differences in the heights of the contact pads 22 of the chips 21 being tested. To compensate for these differences, greater pressure would have to be applied to enable a needle 11 to be able to set up contact with a contact pad 22 that is shorter than the others. However, in this case, such pressure would be too excessive and the other contact pads 22, whose height is greater, would be damaged or even rendered unusable. Furthermore, the difficulty of trueing the needles 11 makes the probe tip card 10 practically impossible to repair.
Currently, the chips 21 are being increasingly miniaturized to a size where the space between the contact pads 22 is also reduced. This space is generally in the range of 200 xcexcm, 150 xcexcm and even less than 100 xcexcm. To adapt to current chips and enable several of them to be tested in parallel, the probe tip cards must have inter-tip gaps of the same magnitude. The needles 11 of the cantilever cards have a conical shape with a diameter that is greater at the ends fixed to the support of the printed circuit. It would therefore be difficult to place these needles side by side. Consequently, a card manufactured according to the cantilever technology cannot be used to test several chips in parallel because it is not cost effective.
A probe tip card made according to the xe2x80x9cmembranexe2x80x9d technology is schematically shown in a sectional view in FIG. 2. A probe tip card 40 of this kind has a flexible printed circuit 41, also called a membrane, fixed to a rigid ring support 45. Metal bosses 42 are made on the flexible printed circuit 41. A bias is maintained on the membrane 41, for example, by a spring 43 held by a lid 44. An electrical contact is set up between the bosses 42 and the contact pads 22 of the chips to be tested when pressure is applied to the silicon wafer 20.
However, to enable constant voltage to be maintained between the metal bosses 42, the dimensions of the membrane 41 must be limited. Furthermore, because of the significantly large size of the bosses 42, the spacing between the bosses 42 cannot be reduced sufficiently to adapt to the small size of current chips. Consequently, the membrane type cards cannot be used to test several chips in parallel. Furthermore, the bosses 42 are all connected to one another by the membrane in such a way that they are not independent. The motion of one boss 42 causes the motion of neighboring bosses 42. The membrane furthermore has great flexibility so that it is very difficult to maintain tension so that the bosses 42 are all parallel and located in one and the same plane. This type of card therefore does not make it possible to easily compensate for the significant differences in height between the contact pads.
Finally, forming a probe tip card of this kind is very costly. Furthermore, given that the metal bosses 42 are made by deposition directly on the flexible printed circuit 41, they cannot be interchanged and the card can not be repaired. Finally, the lifetime of this type of card is fairly limited since it allows for only about 250,000 tests to be performed.
A probe tip card made according to vertical technology has needles positioned vertically, i.e., perpendicular to the surface of the card. Two types of cards are presently being made according to this vertical technology. One is the xe2x80x9ccobraxe2x80x9d card schematically shown in a sectional view of FIG. 3A and the other one is the buckling beam card, schematically shown in FIG. 3B. FIG. 3C provides a schematic top view of one of these probe tip cards made according to the vertical technology for the testing of several chips in parallel.
In these two types of probe tip cards formed according to vertical technology, the probe tips are very thin so that they can be juxtaposed in large numbers. The space between the probe tips may therefore be small enough for the cards to be adapted to the size of current chips. The cards made according to the vertical technology therefore enable tests to be carried out on several chips 21 in parallel, as illustrated in the top view of FIG. 3C. The vertical technology furthermore allows for the cards to be easily repaired since each tip may be replaced independently of the others.
The xe2x80x9ccobraxe2x80x9d card referenced 30 in FIG. 3A includes probe tips 32 that are held vertically between two screens or grids 31, 36. Vertical holes 33 are formed in the lower grid 36 to receive the probe tips 32 therein. The diameter of the holes 33 is wide enough to enable the probe tips 32 to slide vertically. However, the probe tips 32 may become wedged in the screen 36. The smaller the diameter of the probe tips 32, the more difficult is it to form them into shape. The shape of the probe tips 32 are rounded in a first part 32A corresponding to the sliding zone in the holes 33 of the lower grid 36. They are flattened in a second part 32B located between the two grids 31 and 36 to give the probe tips a better spring effect. The probe tips 32 are also formed into a bead shape in a third part 32C called a head, which is located in the upper part of the upper grid 31.
This type of card is generally made on an epoxy or ceramic printed circuit support 34. Holes are formed in this printed circuit support 34 and are each filled with a conductive wire 35 machined and bonded so that it is flush with the surface of the support 34. The wire 35 is lightly gold-plated to allow efficient electrical contact with the probe tips 32. In this type of cobra card, the probe tips are floating. Whenever a pressure is applied to the silicon wafer to press the contact pads 22 against the probe tips 32, each tip is urged against a wire 35. In other words, the head 32C of each tip touches the surface of the gold-plated wire 35 to set up an electrical contact. An hammer effect occurs on the conductive wire 35 and causes the gold-plating of the wire 35 to be dug out. Consequently, the gold-plating of the wires should be repeated very often. This hammer effect is the major drawback of the cobra cards because it considerably reduces their lifetime, which is about 200,000 to 300,000 tests.
Furthermore, in this type of card, the probe tips 32 do not move horizontally, but move vertically so that there is no clawing effect. This clawing effect is necessary to remove the aluminum oxide layer formed on the contact pads 22 of the chips and thus establish a high-quality electrical contact. Consequently, to enable penetration into the oxide layer, the probe tips 32 should have a very pointed end 32D. Furthermore, the probe tips 32 do not have a high heat dissipation. If the current applied to the probe tips 32 intensifies, the probe tips 32 become heated. Since they are surrounded by air, they poorly dissipate heat. Even the holes 33 of the lower grid 36 poorly dissipate the heat.
The card known as the buckling be am card, as referenced 50 in FIG. 3B, has probe tips 54 that are held vertically between three grids 51, 52, 53. In this case, the shape of the probe tips is not formed as in the case of the cobra card, but the probe tips 54 are preformed by the additional grid 52. Furthermore, the probe tips 54 are not floating tips. They are in permanent contact with wires 56 connected to the support of the printed circuit 55. Consequently, the hammer effect is avoided and the lifetime is therefore slightly longer than it is for the cobra card. The buckling beam card enables the performance, on an average, of up to 500,000 tests.
However, at the time of the tests, when pressure is applied to the silicon wafer 20 to set up a contact between the probe tips 54 and the contact pads 22, the probe tips buckle. There is now a major risk that they will touch one another and thus cause a short circuit. Furthermore, the ends of the probe tips 42 have to be very pointed to enable the penetration of the oxide layer covering the contact s to form an electrical contact.
An object of the invention is provide a probe tip card that overcomes the above-mentioned drawbacks related to the different technologies of the prior art. The probe tip card is used to test semiconductor components, while having an efficient compromise among all the conditions to be fulfilled in the requirements. The probe tip card, in particular, must have a high degree of flatness at the ends of the probe tips, high physical independence of the probe tips, and an overall but controlled vertical flexibility. Additional requirements include having a clawing effect to enable the removal of the surface layer of aluminum oxide overlapping the contact pads of the circuits being tested, and establishing a high quality electrical contact. The space between the probe tips must be small enough for them to adapt to the miniaturization of the chips, and it must enable the parallel testing of several chips. The probe tip card should furthermore be easy to repair, have a long lifetime, i.e., allow for one million or more tests, and be a low-cost device.
To meet all these criteria, the present invention provides a probe tip card for the testing of components on a semiconductor wafer comprising a printed circuit support card and a set of probe tips connected to the printed circuit support card. The tips are tilted with respect to the surface of the card and held in this tilted position between an upper grid and a lower grid. The tilting of the probe tips provides the card and the tips great flexibility. Each tip is shifted slightly laterally when a contact pad of a chip to be tested comes into contact with it so that a clawing effect forms a high-quality electrical contact. Due to the fact that there is a spring effect and a clawing effect of the probe tips, it is not necessary to work or form the shape of the tips. This significantly simplifies making the probe tip card.